Image capturing apparatuses such as image scanners, copiers or printers are widely used for capturing or scanning images of documents, photographs or films. As known, the image capturing apparatus usually has an automatic document feeder for automatically and continuously feeding many paper sheets one by one, thereby performing a single-side scanning operation or a duplex scanning operation on the paper sheets fed when the automatic document feeder is operated in a single-side or duplex scanning mode. For enhancing convenience and user-friendliness, these paper sheets are stacked on the ejecting tray in the same order as that of the original stack after the scanning operation.
Referring to FIG. 1, a cross-sectional view of a conventional automatic document feeder is schematically illustrated. Such automatic document feeder is disclosed in for example U.S. Pat. No. 5,784,680, and the contents of which are hereby incorporated by reference. The automatic document feeder 10 of FIG. 1 comprises seven roller assemblies 11˜17, an sheet input tray 18, an ejecting tray 19, a switching guide rod 110, a first transfer path 111, a second transfer path 112, an inclining guide path 113, a guiding plate 114, a switch-back path 115 and an inverting path 116. The first roller assembly 11 includes a pick-up roller. The second roller assembly 12 includes a pair of separating rollers. Each of the third roller assembly 13, the fourth roller assembly 14, the fifth roller assembly 15 and the seventh roller assembly 17 includes a driving roller and a follower roller. The sixth roller assembly 16 includes an ejecting roller 161, a first follower roller 162 and a second follower roller 163. In addition, several image sensing controllers S11˜S15 are used to detect the location of the paper sheet and control the rotational direction of corresponding roller assembly. The locations and operating principles of these image sensing controllers S11˜S15 are well-known in the art, and are not redundantly described herein.
In addition, a scanning module including a slit glass 31, a reflective mirror 32, an exposing lamp 33 and an image sensing controller (not shown) is disposed under the automatic document feeder 10. An exemplary image sensing controller includes a charge couple device (CCD) or a contact image sensor (CIS). When the document to be scanned is transported across the scan region above the scanning module by the automatic document feeder 10, the scanning module scans the document. During the scanning process, the light emitted by the exposing lamp 33 is projected onto the document to be scanned. The light reflected from the document is then transmitted into the optical scanning module through the slit glass 31. After passing through the slit glass 31, the light is successively reflected by the reflective mirror 32, and then focused by an optical lens (not shown). The focused light is then imaged onto the image sensing controller to convert the optical signals reflected from the scanned document into corresponding image signals. The detailed principle of scanning the document by the scanning module is known in the art, and is not redundantly described herein.
Hereinafter, the procedure of performing a duplex scanning operation by the automatic document feeder 10 is illustrated. It is noted that, however, those skilled in the art will readily observe that the procedure of performing a single-side scanning operation will be deduced from the teachings associated with the duplex scanning operation.
First of all, a stack of paper sheets P to be scanned are placed on the sheet input tray 18. Then, a first paper sheet P is picked by the pick-up roller 18, and transported into the first transfer path 111 by the separating roller assembly 12 and the third roller assembly 13. Next, the fourth roller assembly 14, which is disposed at the first transfer path 111, transports the first paper sheet P forwardly to the scan region above the scanning module. When the first paper sheet P is transported across the scan region, the scanning module will scan a first side of the first paper sheet P. Next, the inclining guide path 113 leads the first paper sheet P to the second transfer path 112. Next, the fifth roller assembly 15, which is disposed at the second transfer path 112, transports the first paper sheet P into the gap between the ejecting roller 161 and the first follower roller 162.
At this moment, the switching guide rod 110 is located at a first guiding position as indicated by the dotted line. Next, the first paper sheet P is guided by the switching guide rod 110 and transported forwardly by the ejecting roller 161 and the first follower roller 162 of the sixth roller assembly 16. Next, the seventh roller assembly 17 transports the first paper sheet P into the switch-back path 115, which is defined by the guiding plate 114 and other structure of the automatic document feeder 10. After the majority of the first paper sheet P has been detached from the switching guide rod 110, the switching guide rod 110 is switched to a second guiding position as indicated by the solid line. Then, the seventh roller assembly 17 is reversely rotated to transport the first paper sheet P in the reverse direction. Next, the first paper sheet P is guided by the switching guide rod 110 and transported by the ejecting roller 161 and the second follower roller 163 of the sixth roller assembly 16 into the inverting path 116. Next, the fourth roller assembly 14 transports the first paper sheet P to the scan region through the first transfer path 111. When the first paper sheet P is transported across the scan region, the scanning module scans a second side of the first paper sheet P. For a purpose of ejecting the stack of paper sheets P to the ejecting tray 19 in the same order as that of the original stack, the switching guide rod 110 is switched to the first guiding position again and the first paper sheet P is transported into the switch-back path 115. Next, the switching guide rod 110 is switched to a second guiding position and the seventh roller assembly 17 is reversely rotated to transport the first paper sheet P in the reverse direction. Then, the first paper sheet P is transported into the inverting path 116, the first transfer path 111 and the scan region again. When the first paper sheet P passes through the scan region for the third time, the scanning module does not scan the first paper sheet P. Next, the switching guide rod 110 is switched to the second guiding position and the fifth roller assembly 15 transports the first paper sheet P into the gap between the ejecting roller 161 and the first follower roller 162. Afterwards, the first paper sheet P is transported to the ejecting tray 19. The remainder paper sheets P on the sheet input tray 18 successively implement the duplex scanning operations identical to that for the first paper sheet P. As a consequence, the paper sheets P are stacked in the ejecting tray 19 in the same order as that of the original stack.
However, the process of performing the duplex scanning operation has several drawbacks. As previously described, after the seventh roller assembly 17 is reversely rotated to transport the paper sheet P in the reverse direction, the leading edge of the paper sheet P is successively transported across the inverting path 116, the first transfer path 111, the inclining guide path 113 and the second transfer path 112. If the length of the paper sheet P is too large, the tail edge of the paper sheet P may not be fully separated from the switch-back path 115. When the leading edge of the paper sheet P is transported into the switch-back path 115, the tail edge of the paper sheet P is possibly in contact with the leading edge thereof. Therefore, the paper sheet P is readily jammed in the vicinity of the switching guide rod 110.
In views of the above-described disadvantages resulted from the prior art, the applicant keeps on carving unflaggingly to develop an improved automatic document feeder according to the present invention through wholehearted experience and research.